Question 156391
The average of a set of numbers is the sum of the numbers divided by the number of numbers added up.
Let x = the grade of the fifth exam, so we add the grades of the first four tests to the grade on the fifth test (x) and divide this by the total number of test taken (5), and this is to be equal to her semester average of 82.
{{{(x+82+81+82+75)/5 = 82}}} Add the known scores and then multiply both sides by 5.
{{{x+320 = 410}}} Subtract 320 from both sides.
{{{x = 90}}}
She must have obtained a score of 90 on her fifth test.